Component in a combustion system, and process for preventing slag, ash, and char buildup

ABSTRACT

Disclosed herein is a component in a combustion system comprising a composite, the composite comprising silicon carbide; and a refractory metal silicide comprising a phase selected from Rm 5 Si 3 , Rm 5 Si 3 C, RmSi 2 , and a combination thereof; wherein Rm is a refractory metal selected from molybdenum, tungsten, and a combination thereof. Also disclosed is a process for preventing slag, ash, and char buildup on a surface, comprising disposing a first surface of the composite on the surface; replacing a component comprising the surface with a component consisting of the composite; or a combination thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/054,677,filed 25 Mar. 2008, assigned attorney docket number 228148-1, which ishereby incorporated by reference herein in its entirety.

BACKGROUND

High temperature combustion systems, such as gas turbines, or gasifiersused for the gasification of coal, petroleum coke, biomass, oil refinerybottoms, or the like, generally involve reactions at temperatures in therange of about 700° C. to about 2,500° C., and under pressures as highas 100 atmospheres. Under these conditions, components in the combustionsystems are exposed to reducing environments, corrosive gases andcondensing acids, and are subject to attack by slag, ash, char, thermalshock, or the like, which leads to failure of the components, or of thecombustion system itself.

Some of the problems associated with high temperature combustion systemsis attack by and/or build up of slag, ash, char, or the like, on thesurfaces of vulnerable components, that is, components which are proneto the foregoing. Slag, for example, is highly reactive with metals andceramics. Metal components, such as metal feed injectors designed forhigh temperature gasification processes, suffer from corrosive attack byslag, or by oxygen, sulfur, or the like. Ceramic components, such asceramic feed injectors, nozzle components, shields, or inserts, alsosuffer from a similar attack. In addition, poor mechanical attachmentbetween different components, specifically between ceramic componentsand metal components, tends to lead to mechanical failure of thecomponents, generally due to thermal shock. Component failure leads to,collateral component damage, disadvantageous plant downtime, decreasedreliability over service life, and costly repair or replacement, amongothers. Thermal shock occurs due to rapid increase or decrease inoperating temperatures. Components susceptible to thermal shock, such asnozzles, generally require the inclusion of complex mechanisms, such asactive water cooling, to mitigate failure due to thermal shock.

Therefore, there exists a need for high temperature combustion systemsand components thereof that are highly resistant to chemical attack byslag, thermal shock and fatigue, acid corrosion, reducing environments,and the like. Such a system can operate under high thermal gradientswithout the further risk of mechanical failure. Also, the system shouldbe resistant to fouling due to the deposition of slag, ash, or char.

SUMMARY

The above-described and other drawbacks are alleviated by a component ina combustion system comprising a composite, the composite comprisingsilicon carbide; and a refractory metal silicide comprising a phaseselected from Rm₅Si₃, Rm₅Si₃C, RmSi₂, and a combination thereof; whereinRm is a refractory metal selected from molybdenum, tungsten, and acombination thereof.

In one embodiment, a component in a combustion system comprises acomposite, the composite comprising about 50 to about 85 percent byvolume silicon carbide; about 4.9 to about 25 percent by volume of aphase of a refractory metal silicide selected from Rm₅Si₃, Rm₅Si₃C, anda combination thereof; about 0.1 to about 20 percent by volume of aphase of a refractory metal silicide selected from RmSi₂; and about 10to about 45 percent by volume pores; wherein percent by volume is basedon a total volume of the composite; wherein Rm is a refractory metalselected from molybdenum, tungsten, and a combination thereof; whereinthe composite comprises the molybdenum in an amount of about 45 to about80 percent by weight and the tungsten in an amount of about 20 to about55 percent by weight; wherein the composite further comprises iron in anamount of about 0 to about 2 percent by weight; and wherein percent byweight is based on a total weight of molybdenum and tungsten.

Another embodiment is a process for preventing slag, ash, and charbuildup on a surface, comprising disposing a first surface of acomposite on the surface; replacing a component comprising the surfacewith a component consisting of the composite; or a combination thereof;wherein the composite comprises silicon carbide; and a refractory metalsilicide comprising a phase selected from Rm₅Si₃, Rm₅Si₃C, RmSi₂, and acombination thereof; wherein Rm is a refractory metal selected frommolybdenum, tungsten, and a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein several FIGURES:

FIG. 1 is a schematic diagram of an exemplary combustion system known asan integrated gasification combined-cycle (IGCC) power generationsystem;

FIG. 2 is a pictorial illustration of the wetting of melted slagdisposed on a silicon carbide substrate;

FIG. 3 is a pictorial illustration of the wetting of melted slagdisposed on a silicon carbide substrate; and

FIG. 4 is a pictorial illustration of the beading of melted slagdisposed on a surface of the composite disclosed herein.

DETAILED DESCRIPTION

Surprisingly, the present inventors have discovered that a component ina combustion system comprising a composite, the composite comprisingsilicon carbide, and a refractory metal silicide comprising a phaseselected from Rm₅Si₃, Rm₅Si₃C, RmSi₂, and a combination thereof whereinRm is a refractory metal selected from molybdenum, tungsten, and acombination thereof, is highly resistant to fouling by slag, ash, char,high temperature corrosion, reducing environments, and the like, can bedisposed on a substrate without the risk of mechanical failure, and canoperate under high thermal gradients without the risk of failure due tothermal shock.

There is no limitation as to what type of silicon carbide can be used inthe composite. The silicon carbide can comprise a single phase, or itcan comprise a plurality of phases. The silicon carbide can be coherent,that is, there exists continuity among all the silicon carbide phases.However, the silicon carbide can also be non-connected or can compriseshort connected regions within the composite. In one embodiment, thesilicon carbide comprises a coherent phase. In another embodiment, thesilicon carbide comprises short connected regions within the composite.

In one advantageous embodiment, the silicon carbide comprises shortconnected regions that have a cross-sectional diameter less than about1,000 μm (1 mm). In one embodiment, the silicon carbide comprises shortconnected regions that have a cross-sectional diameter less than about700 μm, more specifically less than about 500 μm, and even morespecifically less than 300 μm. In one exemplary embodiment, the siliconcarbide comprises short connected regions that have a cross-sectionaldiameter of about 5 to about 300 μm.

The silicon carbide can be present in the composite in an amount ofabout 75 to about 98 percent by volume, based on a total volume of thesilicon carbide and the refractory metal silicide. In one embodiment,the silicon carbide can be present in an amount of about 80 to about 95percent by volume, based on the total volume of the silicon carbide andthe refractory metal silicide. In one advantageous embodiment, thesilicon carbide can be present in an amount of about 80 to about 92percent by volume, based on the total volume of the silicon carbide andthe refractory metal silicide.

The refractory metal silicide comprises a phase selected from Rm₅Si₃,Rm₅Si₃C, and RmSi₂. As used herein, “Rm” represents a refractory metalselected from molybdenum and tungsten. A combination of phases, of therefractory metals, or of the phases and of the refractory metals canalso be used. A “refractory metal”, as used herein, is a metal havingextremely high resistance to heat, corrosion, and/or wear. A metal otherthan molybdenum or tungsten can also be a refractory metal, however, itis referred to as “other refractory metal” or “other metal”.Non-limiting examples of other refractory metals include rhenium,tantalum, niobium, titanium, zirconium, hafnium, vanadium, chromium,iron, nickel, and cobalt. A combination of the other refractory metalscan also be used.

The Rm₅Si₃ and Rm₅Si₃C phases are collectively referred to as the“trisilicide phase” or the “trisilicide phases”. These include W₅Si₃,W₅Si₃C, Mo₅Si₃, Mo₅Si₃C, (Mo,W)₅Si₃, (Mo,W)₅Si₃C, and a combinationthereof. “(Mo,W)” refers to a “substitutional solid solution” phase,that is, a phase wherein molybdenum and tungsten are both present. TheRm₅Si₃C phase is further known as a “Novotny” or “Novotnyi” phase.

The RmSi₂ phase is referred to as the “disilicide phase” or the“disilicide phases”. It includes MoSi₂, WSi₂, (Mo,W)Si₂, and acombination thereof.

The disilicide and trisilicide phases are collectively referred to asthe refractory metal silicide or the refractory metal silicides.

The refractory metal silicides can be present in the composite in anamount of about 2 to about 25 percent by volume, based on the totalvolume of the silicon carbide and the refractory metal silicide. In oneembodiment, the refractory metal silicides can be present in an amountof about 5 to about 20 percent by volume, based on the total volume ofthe silicon carbide and the refractory metal silicide. In oneadvantageous embodiment, the refractory metal silicides can be presentin an amount of about 8 to about 20 percent by volume, based on thetotal volume of the silicon carbide and the refractory metal silicide.

Based on the total volume of the silicon carbide and the refractorymetal silicide, in one embodiment, the Rm₅Si₃C phase is present in anamount of about 2 to about 15 percent by volume, and the RmSi₂ phase ispresent in an amount of about 0 to about 10 percent by volume. Inanother advantageous embodiment, the Rm₅Si₃C phase is present in anamount of about 3 to about 12 percent by volume, more specifically in anamount of about 5 to about 12 percent by volume, and the RmSi₂ phase ispresent in an amount of about 2 to about 8 percent by volume, based onthe total volume of the silicon carbide and the refractory metalsilicide.

There is no particular limitation as to the ratio of molybdenum totungsten used in the composite, and this ratio can be adjusted accordingto the desired properties of the composite by a person of ordinary skillin the art. Not wishing to be bound by theory, but it is believed thatan increase in the concentration of molybdenum produces a compositehaving a lighter weight, that is, less dense, and further increases heatresistance to air at temperatures of greater than about 1,500° C. On theother hand, it is believed that an increase in the concentration oftungsten produces a composite having an increased resistance to thermalshock, and an improved compatibility with the silicon carbide.

In one embodiment, the refractory metal silicide comprises about 0 toabout 97 percent by weight molybdenum, and about 3 to about 100 percentby weight tungsten, based on a total weight of molybdenum and tungsten.In one advantageous embodiment, the refractory metal silicide comprisesabout 45 to about 80 percent by weight molybdenum, and about 20 to about55 percent by weight tungsten, based on the total weight of molybdenumand tungsten.

The ratio of molybdenum and tungsten can be the same or different withinthe different phases of the refractory metal silicides. In oneembodiment, the refractory metal silicide can comprise a different ratioof molybdenum and tungsten within the disilicide phases and within thetrisilicide phases.

Thus, in one embodiment, the refractory metal silicide comprises about30 to about 90 percent by weight molybdenum, and about 10 to about 70percent by weight tungsten, based on a total weight of molybdenum andtungsten within the disilicide phases. In one advantageous embodiment,the refractory metal silicide comprises about 50 to about 80 percent byweight molybdenum, and about 20 to about 50 percent by weight tungsten,based on the total weight of molybdenum and tungsten within thedisilicide phases.

In another embodiment, the refractory metal silicide comprises about 20to about 90 percent by weight molybdenum, and about 10 to about 80percent by weight tungsten, based on a total weight of molybdenum andtungsten within the trisilicide phases. In one advantageous embodiment,the refractory metal silicide comprises about 40 to about 70 percent byweight molybdenum, and about 30 to about 60 percent by weight tungsten,based on the total weight of molybdenum and tungsten within thetrisilicide phases.

The composite can further comprise another refractory metal such asrhenium, tantalum, niobium, titanium, zirconium, hafnium, vanadium,chromium, iron, nickel, cobalt, or a combination thereof, with theproviso that it does not adversely affect the composite. The compositecan also comprise other elements such as boron, germanium, aluminum,magnesium, barium, strontium, calcium, sodium, potassium, yttrium,scandium, a lanthanide element, or a combination thereof.

The foregoing other refractory metals and elements can be present in anamount of less than about 10 percent by weight, based on the totalweight of the molybdenum and tungsten, with the proviso that thecomposite is not adversely affected. In one embodiment, the foregoingother refractory metals and elements can be present in an amount of lessthan about 5 percent by weight, based on the total weight of themolybdenum and tungsten. In one advantageous embodiment, the foregoingother refractory metals and elements can be present in an amount of lessthan about 2 percent by weight, based on the total weight of themolybdenum and tungsten. In one exemplary embodiment, the foregoingother refractory metals and elements can be present in an amount ofabout 0.1 to about 2 percent by weight, based on the total weight of themolybdenum and tungsten. In another exemplary embodiment, iron ispresent in an amount of about 0.1 to about 2 percent by weight, based onthe total weight of the molybdenum and tungsten, while the composite isfree of the rest of the foregoing other refractory metals and elements.Not wishing to be bound by theory, but it is believed that the iron isan impurity incorporated during the manufacture of the composite.

In one embodiment, the composite further comprises pores. A total volumeof the composite can be defined as the total volume of the pores, thesilicon carbide, and the refractory metal silicides.

The pores can have a cross-sectional diameter of less than about 1,000μm (1 mm). Specifically, the pores can have a cross-sectional diameterof about 1 to about 800 μm, and more specifically about 100 to about 600μm. In one advantageous embodiment, the pores can have a cross-sectionaldiameter of about 200 to about 500 μm.

The composite can comprise about 10 to about 45 percent by volume of thepores, and about 55 to about 90 percent by volume of the total siliconcarbide and refractory metal silicides, based on the total volume of thecomposite. In one advantageous embodiment, the composite can compriseabout 15 to about 28 percent by volume of the pores, and about 72 toabout 85 percent by volume of the total silicon carbide and refractorymetal silicides, based on the total volume of the composite

In one embodiment, the composite is free of silicon and carbon otherthan those present in the silicon carbide and refractory metal silicidephases, that is, the silicon carbide and the refractory metal silicidecomprise 100 percent of the amount of carbon and 100 percent of theamount of silicon in the composite. For example, the composite can befree of carbon impurities or silicon impurities that are not part of thesilicon carbide phase of the refractory metal silicide phase.

The composite can comprise a low specific electrical resistivity ofabout 0.000001 to about 0.5 ohm·cm, that is, the composite can comprisean enhanced electrical conductivity when compared to other similarcomposites, such as silicon carbide based composites comprisingrefractory metal silicides. While not wishing to be bound by theory, butit is believed that the enhanced electrical conductivity is produced bythe specific ratios of the silicon carbide to the refractory metalsilicides, along with the specific ratios of the disilicide phases tothe trisilicide phases, and the specific ratios of the tungsten to themolybdenum, as disclosed herein.

This enhanced electrical conductivity is an advantageous property of thepresent composite. While the composite can be brazed, soldered, alloyed,or the like, to a substrate, such as a metal substrate, the compositecan also be directly welded onto a metal substrate without the use of anintermediate layer, due to the enhanced electrical conductivity. Whenwelded to a substrate, the composite is in direct contact with thesubstrate, and an alloy is formed at the interface between the compositeand the substrate, which greatly reduces the risk of mechanical failurewhen compared to the same composite that has been brazed, soldered, orotherwise disposed on the substrate.

In one embodiment, the specific electrical resistivity is from about0.0001 to about 0.5 ohm·cm. In one exemplary embodiment, the specificelectrical resistivity is from about 0.001 to about 0.03 ohm·cm.

The composite can be manufactured according to any suitable techniqueavailable to one with ordinary skill in the art for the manufacture ofsuch composites. For example, a hollow form comprising silicon carbidecan be shaped into a desired article, and then filled with therefractory metal silicides, and sintered. Or, for coatings, a coatingcan be formed by alloying the composite constituents using a techniquesuch as electric arc or electric spark. The manufacture of compositematerials is described in U.S. Pat. Nos. 6,589,898, and 6,770, 856.

The composites disclosed herein can be obtained from the Institut FizikiTverdogo Tela Rossiiskoi Akademii Nauk, Chernogolovka, Russia, under thetradenames REFSIC, REFSICOAT, and REFSICUT. The material REFSICUT can beadvantageously used herein.

The component in the combustion system which comprises the composite candefine any component wherein resistance to slag, ash, char, thermalshock, elevated temperature, corrosion, erosion reduction, thermalgradients, or the like, or a combination thereof, is advantageous.Non-limiting examples of such components include a gasifier, agasification feed injector, an injector nozzle, a gasifier thermocouple,a gasifier thermocouple well, a gasifier sheath, an injector barrel, aninjector barrel cooling coil, a gasification feed injector shield, agasifier lining, a gasification radiant syngas heat exchanger component,a gasification convective syngas heat exchanger component, a posimetricpump transition piece, a posimetric dry coal feed pump transition piece,a posimetric dry coal feed pump abutment, a posimetric dry coal feedpump rotor disk, a turbine bucket, a turbine blade, a turbine nozzle, aturbine rotor, a turbine disk, a turbine vane, a turbine stator, aturbine shroud, a turbine combustor, or a combination thereof.

In one embodiment, the composite can be manufactured as a layer, aplate, a ring, a block, or the like, and then disposed on the componentof the combustion system that is adversely affected by slag, ash, char,thermal shock, or the like. In another embodiment, the component of thecombustion system that is adversely affected by slag, ash, char, thermalshock, or the like, can be manufactured entirely out of the composite,and introduced into the combustion system as a replacement part.

In addition, the component in the combustion system which comprises thecomposite exhibits improved wear resistance and/or abrasion resistanceat the elevated temperatures, and can be further advantageous when inaddition to being exposed to slag, ash, char, thermal shock, or thelike, it is also exposed to abrasion and wear. The component in thecombustion system which comprises the composite can have a smoothsurface finish. In one embodiment, the component in the combustionsystem which comprises the composite has a class A surface finish.

One embodiment is a process for preventing slag, ash, and char buildupon a surface, comprising disposing a first surface of a composite on thesurface, replacing a component comprising the surface with a componentconsisting of the composite, or a combination thereof, wherein thecomposite comprises silicon carbide, and a refractory metal silicidecomprising a phase selected from Rm₅Si₃, Rm₅Si₃C, RmSi₂, and acombination thereof, wherein Rm is a refractory metal selected frommolybdenum, tungsten, and a combination thereof. That is, the compositedisclosed above. The composite can comprise a specific resistivity ofabout 0.000001 to about 0.5 ohm·cm. The component can further have asmooth surface finish, and/or a class A surface finish. The componentcan further exhibit improved wear resistance and/or abrasion resistanceat elevated temperatures.

Disposing, replacing, or a combination thereof can comprise, inter alia,welding the composite to a metal substrate, wherein the composite is indirect contact with the metal substrate.

The metal substrate can define the above surface, a component in directcontact with the component comprising the above surface, or acombination thereof.

The component comprising the above surface can advantageously define agasifier, a gasification feed injector, an injector nozzle, a gasifierthermocouple well, a gasifier thermocouple sheath, an injector barrel,an injector barrel cooling coil, a gasification feed injector shield, agasifier lining, a gasification radiant syngas heat exchanger component,a gasification convective syngas heat exchanger component, a posimetricpump transition piece, a posimetric pump dry coal feed transition piece,a posimetric dry coal feed pump abutment, a posimetric pump dry coalfeed rotor disk, a turbine bucket, a turbine blade, a turbine nozzle, aturbine rotor, a turbine disk, a turbine vane, a turbine stator, aturbine shroud, a turbine combustor, or a combination thereof.

Using an IGCC as an example, the composite can be applied to numeroussurfaces prone to slag, ash, and char buildup, or can be used as areplacement component for numerous components comprising surfaces proneto slag, ash, and char buildup. FIG. 1 is a schematic diagram of anexemplary combustion system that would benefit from the incorporation ofthe composite. The exemplary combustion system is an IGCC powergeneration system 50 and is not intended to be limiting with regard tothe type and configuration of combustion system to which the compositeas described herein is advantageously used to prevent slag corrosion aswell as slag, ash, char buildup, erosion and thermal shock. Thecomposite is suitable for any combustion system where slag corrosion andslag, ash, char buildup, erosion and thermal shock are issues. Theexemplary IGCC system 50 generally includes a main air compressor 52, anair separation unit 54 coupled in flow communication to compressor 52, agasifier 56 coupled in flow communication to air separation unit 54, agas turbine engine 10, coupled in flow communication to gasifier 56, anda steam turbine 58. The gasifier interior walls are typically formed ofa ceramic material.

In operation, compressor 52 compresses ambient air. The compressed airis channeled to air separation unit 54. In some embodiments, in additionor alternative to compressor 52, compressed air from gas turbine enginecompressor 12 is supplied to air separation unit 54. Air separation unit54 uses the compressed air to generate oxygen for use by gasifier 56.More specifically, air separation unit 54 separates the compressed airinto separate flows of oxygen and a gas by-product, sometimes referredto as a “process gas”. The process gas generated by air separation unit54 includes nitrogen and will be referred to herein as “nitrogen processgas”. The nitrogen process gas can also include other gases such as, butnot limited to, oxygen and/or argon. For example, in some embodiments,the nitrogen process gas includes between about 95% and about 100%nitrogen. The oxygen flow is channeled to gasifier 56 for use ingenerating partially combusted gases, referred to herein as “syngas” foruse by gas turbine engine 10 as fuel. In some known IGCC systems 50, atleast some of the nitrogen process gas flow, a by-product of airseparation unit 54, is vented to the atmosphere. Moreover, in some knownIGCC systems 50, some of the nitrogen process gas flow is injected intoa combustion zone (not shown) within gas turbine engine combustor 14 tofacilitate controlling emissions of engine 10, and more specifically tofacilitate reducing the combustion temperature and reducing nitrousoxide emissions from engine 10. IGCC system 50 may include a compressor60 for compressing the nitrogen process gas flow before being injectedinto the combustion zone.

Gasifier 56 converts a mixture of fuel, the oxygen supplied by airseparation unit 54, steam, and/or limestone into an output of syngas foruse by gas turbine engine 10 as fuel. Although gasifier 56 may use anyfuel, in some known IGCC systems 50, gasifier 56 uses coal, petroleumcoke, residual oil, oil emulsions, tar sands, and/or other similarfuels. In some known IGCC systems 50, the syngas generated by gasifier56 includes carbon dioxide. The syngas generated by gasifier 52 is thenpassed through heat exchanger 61, which may be of a radiant orconvective design and is used to cool the syngas that exits thegasifiers. The cooled syngas may be cleaned in a clean-up device 62before being channeled to gas turbine engine combustor 14 for combustionthereof. Carbon dioxide may be separated from the syngas during clean-upand, in some known IGCC systems 50, vented to the atmosphere. The poweroutput from gas turbine engine 10 drives a generator 64 that supplieselectrical power to a power grid (not shown). Exhaust gas from gasturbine engine 10 is supplied to a heat recovery steam generator 66 thatgenerates steam for driving steam turbine 58. Power generated by steamturbine 58 drives an electrical generator 68 that provides electricalpower to the power grid. In some known IGCC systems 50, steam from heatrecovery steam generator 66 is supplied to gasifier 52 for generatingthe syngas.

In the exemplary IGCC, gasifier 56 includes an injection nozzle 70extending through gasifier 56. Injection nozzle 70 includes a nozzle tip72 at a distal end 74 of injection nozzle 70. In the exemplaryembodiment, injection nozzle 70 is configured to direct a stream ofammonia proximate nozzle tip 72 such that the stream of ammoniafacilitates reducing a temperature of at least a portion of nozzle tip72.

In the exemplary embodiment, IGCC system 50 includes a syngas condensatestripper 76 configured to receive condensate from a stream of syngasdischarged from gasifier 56.

Advantageously, the composite can be used to substantially reduce and/orprevent build up of slag and/or ash particles. For example, thecomposite can be applied to internal surfaces of the gasifier 56, theinjection nozzles 70 utilized to deliver the fuel and/or oxygen into thegasifier, the heat exchanger surfaces 61 in large heat exchangers intowhich the hot (1,650° C.) syngas passes after exiting the gasifier thatare used for heat recovery and to cool the syngas before it can becleaned, and the like. In the alternative, the foregoing components canbe manufactured entirely of the composite. Advantages of the compositefor heat exchanger surfaces is primarily for anti-fouling, and for thenozzle application, the composite reduces and/or prevents slag corrosionor sticking. As a result, chemical attack by molten slag, glasses,ceramics ashes and the like are prevented, heat transfer throughmetallic heat exchangers surfaces is increased, and plugging of orificesor channels is prevented.

In one embodiment, a nozzle, gasifier, injector, or the like, comprisingthe composite, are operational without the use of a cooling apparatus.

The business benefits are numerous; life extension for components incombustion atmospheres, anti-stick or anti-fouling surfaces in ashcontaining combustion gases, non reactive surfaces for use on componentsexposed to molten slag, increase efficiency for heat exchanger surfacesin combustion gas streams, and the like.

The invention is further illustrated by the following non-limitingexamples.

COMPARATIVE EXAMPLE

In this example, a slag piece was positioned onto a substrate consistingof silicon carbide, and a substrate consisting of silicon carbide, arefractory metal silicide, and carbon in the form of graphite, andsubsequently heated to melting in a high temperature vacuum furnace.FIG. 2 pictorially illustrates the slag piece wetting the former, whichexhibited a reaction with the slag. The wetting angle was about 50°.FIG. 3 pictorially illustrates the slag piece wetting the latter, whichalso exhibited a reaction with the slag. The wetting angle was about35°.

EXAMPLE

In this example, a slag piece was positioned onto a substrate comprisingthe composite. FIG. 4 pictorially illustrates the lack of wetting of thecomposite by the slag piece, which instead formed beads indicating lackof wetting and lack of reaction. The beading angle was greater than 90°with respect to the surface of the substrate, and was about 100°.

This written description uses figures and examples to disclose theinvention, including the best mode, and also to enable any personskilled in the art to make and use the invention. The patentable scopeof the invention is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety unless otherwiseindicated. However, if a term in the present application contradicts orconflicts with a term in the incorporated reference, the term from thepresent application takes precedence over the conflicting term from theincorporated reference.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. Further, it isunderstood that disclosing a range is specifically disclosing all rangesformed from any pair of any upper range limit and any lower range limitwithin this range, regardless of whether ranges are separatelydisclosed. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g., itincludes the degree of error associated with measurement of theparticular quantity).

1. A component in a combustion system comprising a composite, thecomposite comprising: silicon carbide; and a refractory metal silicidecomprising a phase selected from Rm₅Si₃, Rm₅Si₃C, RmSi₂, and acombination thereof; wherein Rm is a refractory metal selected frommolybdenum, tungsten, and a combination thereof.
 2. The component in thecombustion system of claim 1, wherein the composite comprises about 75to about 98 percent by volume of the silicon carbide, wherein percent byvolume is based on a total volume of the silicon carbide and therefractory metal silicide.
 3. The component in the combustion system ofclaim 1, wherein the composite comprises about 2 to about 25 percent byvolume of the refractory metal silicide, wherein percent by volume isbased on a total volume of the silicon carbide and the refractory metalsilicide.
 4. The component in the combustion system of claim 1, whereinthe refractory metal silicide comprises: about 0 to about 97 percent byweight molybdenum; and about 3 to about 100 percent by weight tungsten;wherein percent by weight is based on a total weight of molybdenum andtungsten.
 5. The component in the combustion system of claim 1, whereinthe composite further comprises pores.
 6. The component in thecombustion system of claim 6, wherein the composite comprises about 10to about 45 percent by volume of the pores, and about 55 to about 90percent by volume of the silicon carbide and the refractory metalsilicide, wherein percent by volume is based on a total volume of thecomposite.
 7. The component in the combustion system of claim 1, whereinthe composite further comprises rhenium, tantalum, niobium, titanium,zirconium, hafnium, vanadium, chromium, iron, nickel, cobalt, or acombination thereof.
 8. The component in the combustion system of claim1, wherein the composite further comprises about 0.01 to about 2 percentby weight iron, based on a total weight of molybdenum and tungsten. 9.The component in the combustion system of claim 1, wherein the compositecomprises a specific resistivity of about 0.000001 to about 0.5 ohm·cm.10. The component in the combustion system of claim 1, wherein thesilicon carbide and the refractory metal silicide comprise 100 percentof the amount of carbon and 100 percent of the amount of silicon in thecomposite.
 11. The component in the combustion system of claim 1,wherein the component consists of the composite.
 12. The component inthe combustion system of claim 1, wherein the component defines agasifier, a gasification feed injector, an injector nozzle, a gasifierthermocouple, a gasifier thermocouple well, a gasifier thermocouplesheath, an injector barrel, an injector barrel cooling coil, agasification feed injector shield, a gasifier lining, a gasificationradiant syngas heat exchanger component, a gasification convectivesyngas heat exchanger component, a posimetric pump transition piece, aposimetric pump dry coal feed transition piece, a posimetric dry coalfeed pump abutment, a posimetric pump dry coal feed rotor disk, aturbine bucket, a turbine blade, a turbine nozzle, a turbine rotor, aturbine disk, a turbine vane, a turbine stator, a turbine shroud, aturbine combustor, or a combination thereof.
 13. A component in acombustion system comprising a composite, the composite comprising:about 50 to about 85 percent by volume silicon carbide; about 4.9 toabout 25 percent by volume of a phase of a refractory metal silicideselected from Rm₅Si₃, Rm₅Si₃C, and a combination thereof; about 0.1 toabout 20 percent by volume of a phase of a refractory metal silicideselected from RmSi₂; and about 10 to about 45 percent by volume pores;wherein percent by volume is based on a total volume of the composite;wherein Rm is a refractory metal selected from molybdenum, tungsten, anda combination thereof; wherein the composite comprises the molybdenum inan amount of about 45 to about 80 percent by weight and the tungsten inan amount of about 20 to about 55 percent by weight; wherein thecomposite further comprises iron in an amount of about 0 to about 2percent by weight; and wherein percent by weight is based on a totalweight of molybdenum and tungsten.
 14. The component in the combustionsystem of claim 13, wherein the composite comprises a specificresistivity of about 0.000001 to about 0.5 ohm·cm.